Toward Improved Bioremediation Strategies: Response of BAM-Degradation Activity to Concentration and Flow Changes in an Inoculated Bench-Scale Sediment Tank

Abstract

Compound-specific isotope analysis (CSIA) can reveal mass-transfer limitations during biodegradation of organic pollutants by enabling the detection of masked isotope fractionation. Here, we applied CSIA to monitor the adaptive response of bacterial degradation in inoculated sediment to low contaminant concentrations over time. We characterized Aminobacter sp. MSH1 activity in a flow-through sediment tank in response to a transient supply of elevated 2,6-dichlorobenzamide (BAM) concentrations as a priming strategy and took advantage of an inadvertent intermittence to investigate the effect of short-term flow fluctuations. Priming and flow fluctuations yielded improved biodegradation performance and increased biodegradation capacity, as evaluated from bacterial activity and residual concentration time series. However, changes in isotope ratios in space and over time evidenced that mass transfer became increasingly limiting for degradation of BAM at low concentrations under such stimulated conditions, and that activity decreased further due to bacterial adaptation at low BAM (μg/L) levels. Isotope ratios, in conjunction with residual substrate concentrations, therefore helped identifying underlying limitations of biodegradation in such a stimulated system, offering important insight for future optimization of remediation schemes.

The Growth Yield of Aminobacter niigataensis MSH1 on the Micropollutant 2,6-Dichlorobenzamide Decreases Substantially at Trace Substrate Concentrations

“…First of all, the lower concentrations do provide minimal energy so that cells are undergoing physiological changes turning them into a maintenance state in which the cells hardly grow and might rather convert the available carbon into energy than into biomass. , This situation can be strengthened by mass transfer limitations over the membrane in case of trace substrate concentrations. , Interestingly, Sun et al found that C and N isotope fractionation during BAM degradation in a bench-scale aquifer system inoculated with A. niigataensis MSH1 decreased strongly below 600 μg/L BAM, indicating mass transfer limitations below that concentration. A recent following-up study on the BAM-degrading response of MSH1 to varying BAM concentrations in the same aquifer system suggested that the extent of BAM degradation decreased at lower BAM concentrations, even though a high degradation potential had already been realized at higher BAM concentrations, which strongly aligns with the findings of this study. Otherwise, these observations might be linked with the genetic makeup of the pathway.…”

“…43,44 Interestingly, Sun et al 45 found that C and N isotope fractionation during BAM degradation in a benchscale aquifer system inoculated with A. niigataensis MSH1 decreased strongly below 600 μg/L BAM, indicating mass transfer limitations below that concentration. A recent following-up study on the BAM-degrading response of MSH1 to varying BAM concentrations in the same aquifer system suggested that the extent of BAM degradation decreased at lower BAM concentrations, even though a high degradation potential had already been realized at higher BAM concentrations, 46 which strongly aligns with the findings of this study. Otherwise, these observations might be linked with the genetic makeup of the pathway.…”

Sulfamethoxazole is Metabolized and Mineralized at Extremely Low Concentrations

“…Future investigation of threshold concentrations should entail discussions about the focus on mass transfer limitations or physiological limitations. , In the present study, the biotransformation and mineralization results indicate that SMX uptake into the bacteria and enzymatic activity were not restricted. Isotope fractionation techniques would help to investigate the influence of mass transfer on the rate constants.…”

“…This suggests that the pure strain Microbacterium sp BR1 is capable of metabolizing concentrations down to 0.1 μg L –1 of SMX, which is in the same low range of reported biotransformation threshold concentrations of several other micropollutants: 0.1–3 μg L –1 for 2,6-dichlorobenzamide, 0.4–1.8 μg L –1 for acetaminophen and metformin, 10 and 32 μg L –1 for the pesticide atrazine. 5 , 6 , 30 , 31 …”

“…This suggests that the pure strain Microbacterium sp BR1 is capable of metabolizing concentrations down to 0.1 μg L −1 of SMX, which is in the same low range of reported biotransformation threshold concentrations of several other micropollutants: 0.1−3 μg L −1 for 2,6-dichlorobenzamide, 0.4−1.8 μg L −1 for acetaminophen and metformin, 10 and 32 μg L −1 for the pesticide atrazine. 5,6,30,31 Most SMX removal assays focus on either the fraction of SMX that is depleted or mineralized, without simultaneously considering both the biotransformation and mineralization rates. 14,32 However, the inclusion of both of these rates allows a better understanding of the kinetics occurring at both extremes of the catabolic pathway.…”